There was never any explicit or implicit indication movie that the invasion squad represented the entire alien civilization.

Actually, I take that back...Pullman did say they were like locusts that "consume" every natural resource, so I guess you could argue that since he didn't use the word "procure", that meant they weren't just trying to acquire them for use back home but had to use them for sustenance. But I think the wording is ambiguous enough for it not to be an issue.

While the film does indicate the entire civilization is nomadic, moving planet to planet, at no point does it establish that the Mothership and it's deployed forces are the entirety of that civilization. I'd assume they'll be moving forward on the notion that their civilization is comprised of multiple Motherships, spread out to increase their chances of acquiring resources from suitable worlds (and, perhaps, avoiding conflict over resources between Motherships, etc).

I wonder if they'll be moving towards space combat in these sequels. The earliest rumors of an ID4 sequel over the past 15 years involved Earth retro-engineering alien tech. Clearly the Attacker fighters can go and fight in space. It wouldn't be hard to assume that the City Destroyers can as well- which they would need to since I would assume their typical "deploy, wait, coordinate and attack" pattern would be anticipated this time around. Those superlasers have gotta be able to do some damage from orbit, even if they're not as effective as a low atmo strike.

Well, a civilization could never become a space-faring nomadic civilization without first having been a sedentary civilization, so they undoubtedly have a home planet of some kind. Perhaps an E.L.E befell it and they were forced to go searching for a new homeland?

I assumed that they consumed all the resources on their own world and were forced to seek out others to consume, or some natural balance (a rival or predatory species) that previously kept them in check drove their technological development to the point where they overcame it, leading to the above scenario as their population became unsustainable with their natural drive to consume undeterred during their development prior to the unbalancing.

While the film does indicate the entire civilization is nomadic, moving planet to planet, at no point does it establish that the Mothership and it's deployed forces are the entirety of that civilization. I'd assume they'll be moving forward on the notion that their civilization is comprised of multiple Motherships, spread out to increase their chances of acquiring resources from suitable worlds (and, perhaps, avoiding conflict over resources between Motherships, etc).

"I saw his thoughts. I saw what they're planning to do. They're like locusts. They're moving from planet to planet... their whole civilization. After they've consumed every natural resource they move on... and we're next"

The only thing that they spread out would be their recon scouts, three of which were unlucky enough to crash their plane in Roswell. The others make it back to base, report that the planet is habitable, the population is technologically inferior, and are both still busy trying to reconstruct from the last big war while being on the cusp of starting a brand new one.
The invaders did their research, then decided to move their entire civilization to Earth. If there is another ship, it would have been following close behind, and would most likely be strictly for colonization. The military goes in and takes control and makes it safe for the rest of them.

They just weren't counting on Apple software being compatible with their computers.

Well, spreading out is just my speculation of how the sequels will treat it if they take the multiple-ships approach. Having multiple ships doesn't negate this p[articular Mothership being the one sent to us "next".

You know, sort of a "Mothership 199-6, you've got the Sol III assault. Mothership 199-7, you get Andromeda IV..." etc.

Wow, you read an awful lot into a light-in-thought summer block-buster movie. I don't think the writers had that much thinking invested into the movie.

Well, that statement is only reading into it so far as to theorize how an advanced civilization such as theirs could have developed and continued their locust-like behavior.

That said, I admit I put a lot of fan fic analysis into ID4 back in the day, writing my own fan tech manual for it (at least partially, never finished it, IIRC). At the time, it was the best thing since Star Wars, and contributed to my interest in movies, trailers, wav trading and Apple Quicktime, so I was eating it up.

Even made some ID4 custom card images in the style of the SW CCG (yes, theyre terrible and involve some injokes like "trivia master" skills, but it was fun):